Below we describe proposed changes to the AIDA interfaces
together with some discussion. Changes are based on our experience with current
version of AIDA and attempts to extend it.

General
Suggestions:

1. Filters.

It
would be useful to have an "enable/disable" and "invert"
switches for IFilters:

public
interface IFilter

{

...

// New methods

public void setEnabled(boolean
state);

public boolean isEnabled();

public void setInverted(boolean
state);

public Boolean isInverted();

}

There
should also be a convenient way to apply analysis cuts not only to ITuple, but
to a IHistogram and ICloud as well - imagine fitting function to a histogram
and excluding tails from the fit. Also more flexible cut manipulation is
desired: dynamically add more cuts and remove some of previous cuts. One way to
do it is to create cuts that don't depend on an ITuple and include
"add/remove" methods in the ITuple interface:

public
interface ITuple

{

...

// New ITuple methods here:

// can add as many filters
as you like, they will be applied

// sequentially in the
order they were added

public void addFilter(IFilter
filter);

public void removeFilter(String
name);

public void removeAllFilters();

// Returns array of filters that
are currently added to the ITuple

public IFilter[] filters();

}

public
interface IFilterFactory

{

public IFilter create(String
name, String script);

}

This
way has one disadvantage though - one has to assume what filters are attached
to ITuple - filters are not passed to the "client" explicitly. So it
may happen that some filters added (or created) earlier are forgotten and
can have an unexpected effect.

User
should be able to manipulate IFunctions: add, multiply them, maybe even
convolute two functions. Registering user-defined function with AIDA
IFunctionFactory on the fly also seems like a nice feature. Also ability to
generate a set of numbers according to a given distribution can be useful in
fit cross-checks and toy Monte Carlo studies.

public
interface IFunctionFactory

{

...

// Allows user to register new
function factory

// IUserFunctionFactory should
have method "String[] types()" that

// return all IFunction types
that this user factory can make

public void register(IUserFunctionFactory
userFunctionFactory);

// Do arithmetics with functions,
Example: "add" f_new=c1*p+c2*(1-p)

// Note that "div" does
not make much sence for PDFs

public IFunction add(IFunction
f1, IFunction f2, double p);

public IFunction add(IFunction[]
f, double[] p);

public IFunction mul(IFunction
f1, IFunction f2, double c);

public IFunction mul(IFunction[]
f, double c);

public IFunction div(IFunction
f1, IFunction f2);

}

Another
useful feature would be ability to generate set of random numbers distributed
according to a given function:

// Create ITuple with one column
and nEv rows, filled with random numbers

This
method can be put in the ITupleFactory as a convenience method, or it can be
implemented in some additional package (say hep.aida.util), as this
functionality can be achieved by using already defined AIDA interfaces.

There
will be more about IFunctions in the Fitting Proposal section.

6.
Plotting

Configuring
plot attributes, like histogram statistics, function parameters, fit results is
a complicated task. One way to simplify it would be to associate some
"hash-type" object (like IAnnotation, maybe) with any plottable class
(IFunction, IHistogram1D, ...) and mark items there as "displayable"
or "non-displayable". Displayable items then will be picked up and
displayed by IPlotter.